(1) Field of the Invention
The present invention relates to a transmission system for control information in a communication network and, more particularly, to a control information transmission method suited for a communication network having a plurality of nodes interposed in one information transmission route and a transmission system therefor.
(2) Description of the Prior Art
The communication network in which at least one relay node is interposed between a node acting as an information source station and a node acting as a destination station is required to have a technique by which each node is enabled to grasp the state of a connection link or an adjacent node. In the communication network of this kind according to the prior art, according to Japanese Patent Laid-Open No. 52143/1985, each node (or a packet exchanger) is enabled to notify periodically an adjacent node of its own state so that it can detect the state of the adjacent one on the basis of the periodicity of the notice of the state.
In the communication network of the prior art, sufficient consideration is not always taken from quantitative reduction of the control information such as the aforementioned state notice packet to be transmitted between the nodes.
For example, let the communication network be assumed, in which two nodes N.sub.1 and N.sub.5 are connected by a communication route R which is composed of relay nodes N.sub.2, N.sub.3 and N.sub.4 and information links l.sub.1 to l.sub.4 as shown in FIG. 14. It is also assumed that all the information links be connected and that a communication route be established between the nodes N.sub.1 and N.sub.5. If, in these states, the information link l.sub.1 is troubled, the node N.sub.2 detects the trouble and generates a fault notice packet. The terminal node N.sub.5 is informed, when it receives the packet, of the fact that the communication route R to the node N.sub.1 has been disconnected so that it cannot communicate with the node N.sub.1. If, at this time, another information link such as the link l.sub.3 is troubled, the node N.sub.4 also performs operations similar to the aforementioned ones to transmit a fault notice packet. However, this additional packet is useless for the node N.sub.5 which has already be informed of the fault of the route R, and this means that waste control information for the communication network has been transmitted.